Digit registering means responsive to selective frequencies



H. M. BASCOM ET AL D IGIT REGISTERING MEANS RESPONSIVE TO SELECTIVE FREQUENCIES Jan. 27, 1948.

Original Filed Jan. 15, 194:

3 Sheets-Sheet 1 FILTER /2/9 H M. BASCOM FRANCIS A. HUBBA INVE N TORS GENE V/E VE M HUBBARD l-l/S EXECQTR/X A TTORNEV Jan. 27, 1948. H. M. BASCOM ETAL 2,434,898

DIGI'I' REGISTERING MEANS RESPONSIVE TO SELECTIVE FREQUENCIES Original Filed Jan. 13, 1943 3 Sheets$heet 2 BY 63am A TTORNEY DIGIT REGISTERING MEANS RESPONSIVE TO SELECTIVE FREQUENCIES Original Filed Jan. 15, 1943 5 Sheets -Sheet 5 INVENTORS: H 84560 FRANCIS A HUBBARQ'DECEASED GENEVIEVE M HUBBARD HIS EXCUTRIX ATTORNEY Patented J an. 27, 1948 DIGIT REGISTERING MEANS RESPONSIVE TO SELECTIVE FREQUENCIES Henry M. Bascom, Maplewood, N. J and Francis A. Hubbard, deceased, late of Maplewood, N. J by Genevieve M. Hubbard, executrix, New York, N. Y., assignors to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Original application January 13, 1943, Serial No. 472,202. Divided and this application January 16, 1946, Serial No. 641,592 1 7 Claims.

This invention relates to telephone systems and more particularly to a system employing a call transmitter of the type forming the subject-matter of our application, Serial No. 472.202, filed January 13, 1943, which issued July 9, 1946, as Patent No. 2,403,475, and of which application this application is a division.

This transmitter is provided with three vibrative elements which may be selectively released for vibration either during the down stroke or the up stroke of an operated key-set key, The studies which have been made of the time interval required for the satisfactory registration of signals transmitted by a substation transmitter of the reed type and observations of the speed with which the keys of the key-set are operated indicate that it would be possible to generate a si nal impulse which could be registered accurately on either or' both the down stroke and the up stroke of a key-set key. In receiving circuits which have been developed heretofore for use with a call transmitter of the type disclosed in United States Patent 2,315,344 granted March 30, 1943, to R. F. Mallina, a signal duration of 20 to 25 milliseconds is all that is utilized for effecting a registration of such signal the major portion of the signal being consumed inthe functioning of the unit of the receiving circuit, which indicates that a signal is present and which activates the receiving channels of the receiving circuit for a period of five to eight milliseconds. Since it appears to be unusual for a key stroke to be completed in less than 100 milliseconds, it is therefore entirely possible to receive two separate signals on each key stroke.

The principal advantage which is gained from this method of operation is that the number of vibrative elements may be reduced from five to three, since the selective release of the three members may be made first during the down stroke of any key to send one signal impulse and again during the up stroke of the key to send a second signal impulse. The reduction of the number of vibrative elements enables a corresponding reduction of the number of receiving channels required in the receiving circuit at the central oflice. This reduction permits the frequency spacing between channels to be doubled for the same outside frequency range which would reduce the discrimination required between channel surface. For example, the channels could bedesigned to be responsive to signals of the three frequencies 700, 1,100 and 1,500 and, of course, the vibrative elements of the call transmitter would be selected to cause the generation of such frequencies. Alternatively, the outside frequencies could be made smaller so that the difference in attenuation between the highest and lowest frequencies would be less.

It is therefore an object of the present invention to enable the registration of any digit in response to two successive impulses of selected frequencies.

It is a further object of the invention to reduce the number of signal frequency receiving channels necessary to respond to the signal frequencies selectively transmitted in accordance with any keyed digit.

A further object of the invention is to provide a greater discrimination by the receiving channels of a signal receiver which are responsive to codes of impulses of selected frequencies.

These objects are attained by the provision of mechanism in a call transmitter of the type disclosed in our parent application hereinbefore referred to, whereby the operation of any one of the ten keys of the key-set is effective upon the down stroke to selectively release one of three vibrative elements or reeds and is effective upon its up stroke to selectively release one or more of the three vibrative elements, In this transmitter only three vibrative elements or reeds are required.

The selective releasing of the reeds in response to the down strokes and up strokes of the ten key-set keys causes the generation of signals of the three frequencies a, b and c which might. for example, be of 700, 1,100 and 1,500 cycles irequency.

A code may be so selected with respect to the standard arrangement of the keys in the key-set as indicated in a table appearing hereinafter that every key releases a single reed on the downstroke and that no two adjacent keys arranged either vertically or horizontally release the same reed on the down stroke. Hence, if two keys are depressed at once, two reeds will be released and the receiving circuit can be arranged to recognize this as a false signal.

The transmission of two signal impulses by the call transmitter for each keyed digit requires a modification of the receiving circuit associated with the central office sender whereby three receiving channels are provided to receive the three different frequencies transmitted by the call transmitter with each of which channels two groups of recording relays are associated. Each of these groups of relays comprises a relay corresponding to each of the three frequencies, one group being normally associated with the three transmitted upon the up stroke 'ofithexoperatedilor key. Thus upon the termination: f-fth'eetwooime pulses of the digit signal a relay ofitlie first group' and one or two relays of the second group will remain operated to control thee'settingiofa.digit. register of the sender.

For a clearer understanding of the invention; reference may be had to the following detailed description taken in connection with the accom panying drawing in which:

;Figs-.:jl,.;22.;and 3:;takemtogether, sl'mWqfiz-xtslfi: phonezsystem inraccordanceewith.the;present=.in1 vention'ito; wl'iichi'lthechnpro edicall transmitter is applicable; Fig. 1 showingrtheesubstatiomcire cuitunxwrnch:thezcall.itransmitterriseinstalled; a diagrammaticqiilustration;rot-raulinwfinder: first selector; :aasenderalinkrcomprisingjatrnnk finder and a sender selector, and a portion ofsthezcir-e cuitrofiamentral :ofiicesendert ili'igg 2 zshowingzthe receiving rchannelsmoizzthe sender,i1the..:recording 'relay:rain-diether:. control relays; zand fligefiwshowcertain rofa the senderr registers-:andiprogress relays associated therewith; and Ffigmiis .a diagram) showinga'how Fiigs; 1.12:; and :3zsho1ild. be arrangedi-tmfnllyrdiscioseithezinventiom.

The:keyszofitheikeyeset;:whiclrlmamforsrefere nc purnosessbesdesignatedlel atuiKzl fltiinclusive. :arezsordesigned wthatvzthey rare: efiectiire rtorcontrci .thexgeneratiomofzcurrentiofzthe :frequencies :beand. 1c:in :the :mannerzindicated; imthezfnl-lowe 'ingtable:

ma 21:1! 21:2; 3; ",K4: 2

Down-strokeelirequency ;a.' ".20 'ibf; 1 m u UpstrokeFreguency: ta 3 v.cr 1.12. t:

Key K6 K7 K8 .iKili ZKIO Down-strokeFrequencm l 5c 7 J) i .m i 5b? z: Uprstrokefrequencyiu a... .a c. c. bet-n Thecall. transmitter of foul parent patentherestofore referred to, is applicable to a Wide variety oi @types .of dial switching.systemssand, iparticularlyrto .those: QLtheQtype-in which register 11116.31): anisms/are employed at rthercentraliofi'ice for registeringthee designation ;transmitted and; .for controlling-1; the 2 selective. operation rofiautomatic switches to .complete (connections-s. Accordingly, .thersystem chosen to .illustratethe invention :is .onecinmhic-h 'thecentral oifice is. equipped-with automaticswitches..ofnthe panel-;ty .e and with register senders for iregistering. the designations transmitted to the-central officetfrom subscribers stationss. It twill-hec-obvious that-.othenformsnof switchescw-mayabe. used sfor-iestablishinggthescone nections: such iastswitchessofi the cross har (type (and: switches of! the-well-known ,stepeby-step 122138..

.Referring to-Eiga L '2 and. 3. of :the. drawings, in :Which .areference.- characters: rcorrespondingeto those: designatingizsimilar -apparatus elements 'in li igss 12,13 and lA-iofzourgparent patenthaue-heen applied; :a subscriberis --li=ne is eshown aipearing in the contact bank of the line finder LP. The

lineefindenisejolned to .aaflrst. or district. selector Siand theseetwo:switch'esstogethenform a. link for extending subscribers lines to trunks extending :to other selectors (not shown) by which a connection from a calling subscribers line may be extended' to a' wanted subscribers line. The line findr 'a-nd district link have access through a senderlink=SLcomprising a trunk finder TF and :fiinSElldlEl'FSE-kifltfl]? SS to a plurality of common iregristerisendersr Figs. 2 and 3 disclose such parts io'fia'.sendercasareanecessary for an understanding'zoft the -prtesent invention. The number of registers employed in these senders will vary with therequirements of the exchange areas. In some threer-oficm Bfidefi'dlglt registrations and the numerical part of the designation usually requiresriour registrations. In the present disclosure three oflice code digit registers A, B and .C, are-shownin sl ng. :3-.and the units-numerical register UriS :alsov shown-lit:beingmnderstoodihat thetthousands, .hun dreds eand-tens-rregisters would bezprovided anda-inserted betweernthe units =regis+ ter :U;and-,the mode: digit register These reglstersreachtcomprise five registererelays which are selectively operated .underethev control of -.the sixrecordin g .relays.AD,.BD, QD, AU, BU, andCU, andthe frequencyxeceiving ohannels.-Fa-, Eb and EmofEigiZ It will the assumed-that. theisubscriber. at -the substation illustratediniEigsliremoves the handa set .H.,of.-the subset from the eradleeto initiate :a call whereupon a circuit-ziswestablishedr over::the substationi line to the -central. offiee-whichlzis instrumental .in..causing- -rtheline-,finder; :to hunt. for: and. establish a connection with the calling. .line, whereafterr the: line-finder: ifirst selector .-link .hecomes iassociatedlover theesender linkSL comprising the trunk-finder anchthe sender-selector. SS withi-ant-.idlesenderi Upon the. association .of v'the "sender: with.the:substation a.circuit.is established rfrom-batterymver brushes of thetrunkfinder TEandrsender selector SS, conductor. 1200 and. 'WiH'diHQSx-Ofs113163 6113101! itb round. iRelay I 3 operates: and. closes an rob vious operatingcircuitdonrelay -.l 3.0-2; Relay 1 3ll2 upon operating-Z .connects-gipundn overnits right .contacts to.-the roii-rnormal conductor: [13.63 to .providedockinge ground for other :rela-ys: of the sender and .over. ;its-- left 1 contacts and condu-c'tor 130111 establishes the circuit 0f i'relay 129 l With ground-connected -to.--conductor- 1| 3133 1a circuitis established therefrom over the-left :back contact of relay I 3891ald B0nduCt0rc|3H1 to :battery through @the windingqof :progresslrelay. I 486, whereupon relay-1M '6 :operates-andflocksinra :cir-' cuit. from .battery. through {its winding rand: the winding; ofgprflgress: relay. 4401; ;over the inner left front contactsaof; relay l406vand over -the back. contact of progress :relay I41 to ground ion conductor 41303.. .Relay +40 1 does :not". operate :in this lockiflncircuittsinee :itsawilldi'ngis; shunted soJong as ground remains'connectedto conductor .l3l10t. When -r.elay: l lflfiioperatesxa :ci-rcuit iis::-also established :frornt; ground on :conductor: 1:383, ;.over the back contact of;relay- |4l l, ithe outerile'ftccon tacts-of relay |=406',-conductor l 31 I and-to battery through :the rig-ht normal contacts and windin .otrelayliiflfi: Relay-i I309: thereupon operates, 10 cksr over 'its :right alternate :contacts to; ground on conductor 4303: and JaZt itS back contact removes. ground from conductor I310 whereupon -relay--l 40 1 operates'in zthe .leck-ing; circuit oizrelay 14,06; prepares.- operating .circuits :for: the relays of the first code digit register A over conductors I33I I332, I334, I335 and I330 and at its right contact connects ground to conductor I30I to shunt the right winding of relay I300 whereby the current flowing over the operating circuit of relay I300 is increased as a signal to the linefinder selector link.

' Relay I20l upon operating connects the windings of battery feed relay I202 to the calling line substation over a circuit which may be traced from battery through the left winding of relay I202, the left contacts of relay I20I, brush I203 of sender selector SS, brush I204 of the trunk finder TF, contacts of sequence switch cam I205, brush I206 of line finder LP, the ring conductor of the calling line, switchhook contacts I201, the back contact of the ofi-normal switch assembly 9, through the transmitter I208, the left winding of repeating coil I209, the tip conductor of the calling line, brush I 2I0 of the line-finder LF, sequence switch contacts I2I I, brush I 2I2 of trunk finder TF, brush I2I3 of sender selector SS, right contacts of relay I20I, right winding of relay I202, normal contacts of relay I2I4 to ground through the secondary winding of the dial tone coil I2I5. Relay I202 operates over this circuit and dialing tone current is applied thereover to apprise the calling subscriber that he may proceed to key up the digits of the desired telephone number. Relay I202, upon operating, establishes an obvious circuit for relay I2 I 6 which also operates to prepare an operating circuit for relay I2 I 0, and relay I202 establishes a circuit from ground over its left contacts, conductor I2II, over the upper normal contacts and through the winding of relay I305, and through resistance I301 to battery. and in parallel therewith through the winding of relay I306 and resistance I308 to battery.

Relay I305 operates and looks over its upper alternate contacts to ground on conductor I303 but the winding of relay I 306 being shunted so long as ground is applied to conductor I2II, does not operate. The closure of the lower front contact of relay I305 is without function at this time.

In response to the reception of dial tone the calling subscriber proceeds to key up the digits of the wanted line number, which number it will be assumed is 01-13-4067. When the key K2 which, in addition to the digit value 2 has the letter designations ABC, is depressed to transmit signal impulses for the first code letter C. the offnormal switch assembly 9 is momentarily operated and then released during the down stroke of the key and in the interval that the movable contact of such switch assembly is in engagement with the front contact thereof a reed of the generator G is caused to vibrate to generate a current impulse of a predetermined frequency. Again when the depressed key is released, the offnormal switch assembly 9 is momentarily operatedand released and during the interval that the movable contact thereof is in engagement with its front contact, a reed will be vibrated to generate a second current impulse of a predetermined frequency. By referring to the preceding table, it will be noted that when key K2 is depressed, the frequency is generated both upon the down and up strokes thereof. This frequency might, for example, be of 1,100 cycles.

The movement of the movable contact of the off-normal switch assembly 9 from its back or normal contact position disconnects the subset transmitter I208 from its bridged connection across the substation line and the engagement of the movable contact with the front contact connects the coil 35 of the call transmitter generator 6. G across the line through the condenser I2I0. There being no direct current bridge across the substation line at the substation so long as the movable contact of the off-normal switch assembly 9 is out of engagement with its back contact, relay I202 of the sender releases in turn opening the circuit of relay I2I6 and removing ground from conductor I2II. Relay I2I6, however, being slow to release does not release during the interval that the movable contact of the off -normal switch assembly 9 is disengaged from its back contact. With relay I202 released and relay I2I6 operated an obvious circuit is established for relay me which operates and at its contacts disconnects the secondary winding of the dial tone coil I2l5 from the calling line loop to discontinue the application of dial tone current thereover and connects direct ground to the calling line loop. The removal of ground from conductor I2II removes the shunt fromthe winding of relay I306 which now operates in a circuit from ground on conductor I 303, over the upper alternate contacts of relay I305, through the winding of relay I306 and resistance I308 to battery.

When the first impulse of current of the frequency c is transmitted over the line, it passes over the previously traced circuit through the sender link, through the broad band-pass filter I2 I 9 and the primary winding of the transformer I220 and is impressed through the circuit X and the primary windings of the input transformers associated with the receiving channels Fa. Fb, Fe and V. Associated with each input transformer, such as I 3| 3, is a frequency receiving channel consisting of a secondary winding of such transformer, a series tuned circuit I3I4, a single vacuum tube such as I3I5 with a feedback through the copper-oxide units, such as I3 I 6, and

a relay, such as I3I'I. Initially, the vacuum tube is biased nearly to cut-off. A small received signal is amplified and fed back through the condenser I3I8 and the copper-oxide units I3I6 to charge up the condenser I3I9. This condenser is poled to reduce the negative bias on the grid of the tube I3I5 with the result that the gain of the tube is increased and the amount of voltage on the grid is increased further. The final result is that a relatively small signal is sufficient to produce a sharp rise in plate current through the relay I3I I. The sensitivity of each individual channel is adjusted by means of the variable resistance. such as I320. This method controls the sensitivity by changing the alternating current feedback and does not affect the tuning of the channel.

From the preceding description it will be apparent that each relay. such as relay I3II in each channel, will respond to a single frequency with a relatively high discrimination against the others. In the present description it has been assumed that the first channel Fa is tuned to t e a frequency of 700 cycles; the second channel Fb is tuned to the 1) frequency of 1,100 cyces; and the third channel F0 is tuned to the 0 frequency of 1.500 cycles.

Upon the receipt of the first impulse of frequency c the channel Fc responds resulting in the operation of channel relay I3I'I. Relay I3II upon operating establishes a circuit from ground over its contacts, the middle right back contact of transfer relay I32I, through the winding of recording relay CD to battery. Relay CD thereupon operates, looks over its inner left contacts to ground over the back contact of release relay I322 and at its outer left contacts prepares a circultaforrrelay I324. Upon theetermination of. the: signal; impulse: when 1 the ofi-normal switch assemblyfl'n'eestablisheslthe direct current bridge. atttheisubstation through the subset transmitter, relayalfllliereoperates t -;establish the circuit of relay-A21finandztoureconnectground to conductor I:2il :I cwhereupon such ground is-e-xtended over the upper front-contact or relay I-305-to a point betweerrthe winding offrelay- I305 andresistance I 30z'h, Relay5..--I:305. bein -how shunted releases. Relay 1l-305ei$y howeren-maintainedoperated follewing -stherreleaseaon'relay 4305- over a circuit fmmzgroundi on conductor I217,- over the upper normal:contactsyofnelay I 3n5,-through the windimgcofilrelayi I 3flfi,'- ,and:reSistance-I308 to battery. Witty-relay --I-305 -,released?:and relay I 306 held operated theycircuitof relay I32I is now completed:fromxj yound over the lower back .contact; f: relay-I305 the. inner lower front contact oti'relayf I306; theeouter left contactsof relay- CD toabattery. through the: winding .of relay I32 I anelay I32I now operates; locksover its inner right front contactto ground-over theback contact of relay I 322; at-.its shack contacts disconnectsethetwinding-s. of recording relays AD, -BD and-1CD: :fromrthezcontacts, ortheschannel relays 1323,; l 324 randvt3 III, ;respectively; connects the windings oirecording relays AU, BU and CU witlznthelcontactsz of 2thechannel relays, all of whichlaresahthis time released and at its-outer .mghtirontmontact ,prepares acircuit for relay 'zDnring lthe transmission of ,the second signal 'imp,ulse-,1a-ssinned-to:be alsoof the frequency cmtheaofienormalrsn m assem ly 9 being again operatedmomentari-ly, relay I202 again releases toziremoyelground from conductor I211 thereby releasing relay-I306. :Ghannelcircuit Fcagain respondsvtovthe;receiptof the frequency and the; channel relay I3 I I =upon operating and with transfer relay l 32 I roperated-establishes a circuit from ground: overethel contacts of relay I 3 I I, the middlecrig'ht ,-.front contact of-relay I32.I to batteryithrough'lthewinding'of recording relay CU. Relay:CU,ruponioilerating.locks over-its left-front contact to ground over .rthe backcontact of relay [3221 Whenithe .ofienorma-l springassembly 9 .again releases: to: terminate the second I frequency impulsez the=reoperationotrelay I305 over the .c-ircult;previouslyv traced dsefiected by the reoperetionzof-relay.-*I202. With relay I305 operated and-relay; (I 30.6;unoperated lacircuitisestablished from ground-overithelower front-contact vofrelay I305, the lower back contact of relay I306, the rightzback contact-:otvre'ayAD, the No. 2 .right :b'ack .;contact of relay; BD, the, No. 2 v rightfront contact 10f operated relay. CD thelNo. 2 right .back contactcof relay AU, ,the; No; 3 right back con- ;tact of :relay; --BU, the-No.15. right front contact :ofiuperated relay CUyCQHdHCtOI1332; the. No. 3 le'ftacontacts of progress-relay 100 I, to battery throughthe :right-- windingof relay I 402 of the :A: code dig-it register; Relay 1402. thereupon operates and locks over its left winding andleit contacts itoiground on rconductor 1303 and with lthegrremainingc-relays IMlI ,160.4, I405 ,andMllll co'fj. thevzAzregister :unoperated; serves to register 'itherfirsttofilce'eode letterrG;

.Aicircuit 'is :alsorestablished 3 upon the operation :ofrelay "-I305 :0ver-;its:lower front contact, the lower backixcontact-of.relay: I306, over-the-outer right'i-front contact, of'reiay- 2'I32I to battery through ithe .windingsaofxrelay I322, which. operates waiter; .an:tinterval:suffibientctoyinsnre ,ithat thejdigit signals recorded through the .operation Ofrecording. relays have been efiectiveto .cause the: registration .thereof in :a digit register, of the. sender; atnits back. .contactopens the locking.

, circuits-of the operated recording relays,,. .in the case assumed relays CD and CU, which .there-f upon-release; opens the .lockingicircuit: of transferrelay. I32 I= which releases and at ,itsfront contact .establishes-.an obvious .circuit .for relay I325: Relay, I325 operates,- locksloverl. its right contacts tooff-normai ground on conductor I303 and at its left contacts ;.prepares.. a. circuit-v for operating'the. progress relay IIIIG. Whenrelay- I321 releases, relay-I322 talso releases.v

When the subscribendepressesthe .key Kflnto transmitimpulses for the second oilice code letter H. which has anumerical value of 4, theoff-j normal switch .assembly. 9 is operated .momentarilyto open :the direct current loopatthe-sube station andto :connect the, generator .G .toJzhe substation line. During the interval that. the switch :is thus. operated the reed. Rois releasedQto transmit an impulse of the frequency. .0 which, upon :being receivedgin the receiving. channelIEc of thesender. resultsinthe operation ofmhannel relay I 31 Land, with transfer relays I32-I. now released, .in .the operation of. recording-relay. .CD over' the circuit. previousPy. traced. Relay; CD upon-operating locks under the control ofrelay I 322.- andprepares the circuit of..relay.,l32I as previously described. .When. the line .loop. is opened atthe substation by theofi-normalswltch assembly, relay I 202..- releasesand by. removing ground from conductor. I2 I] .permits. relay, 1.305 to Operate in. the manner previously. described. With relays-I 305,.and I 30fi.now-both operated and relay I 325- operated, a circuit. is established .from ground -over the lower.frontcontactofirelay.I305, the lower .front. contactof relay. 1305,, the left contacts-.01 relay I325, conductor .I.3I 2, -,the.,right front contact of progress relay. I400; to...battery through the winding.of=progress..relayl-I 4 I6 .which operates .and looks through itswinding andthe winding of progress relayl 4 I! over the left contacts. of relay. I IIS andtheback. contact. of progressrelay I 42.1 A to ground onconductor .I 303. Relay IIIIl beingshunted solong. as ground re.- mainsconnected to, conductor I312, ,does, not operate.

At. the end of thefirst. impulse .for.;the1s.econd code digit, withthe loll-normal switch assembly 9 restored, the transmission of the frequency..c ceases; channel relay =I3II releases, and the ,die

root-current loop isereestablished,at-the substae tion resulting in. the reoperation-ofrelay 1202 and the reconnection of ground .to..-conductor I211. Asbefore described relay 130.6:isnow held operated'tto this ground andrelay 1305 .isshunted and-releases. With relay I.3.05..released.and relay; I306 operated, the circuit-.fortransfer. relay I32 I previously prepared through the opera? tion .of 0 recording relayv CD, is completed .and re?- lay I32I operates and locks, as..previouslyde= scribed under the control of relay, I 322; Relay l3il5puponreleasing also removes ground from conductor 1312'whereuponsprogress relay I'M] operates 'in the locking; circuit of relay] 4] Ii, com nects the windings-ref the relays of-the B,.code digit register to conductors I 33 I, I332, 1.334,;I335 and I330, extending to contacts-of therecording relays and atjits. right back contacts opens. the locking circuit-of relays HIDE-and;Idfllwhichnow release since their I operating circuit was opened .upon the previous operation .of relay -I 309.,

' Upon theauprstroketoiethe -oepressedikeyiKll the off-normal switch assembly 9 is again operated momentarily to open the direct current loop at the substation and to connect the generator G to the substation line. During the interval that the switch is thus operated the reed Rb is released to transmit the frequency b which upon being received in the receiving channel Fb of the sender results in the operation of channel relay I324 and, with transfer relay I32I now operated, in the operation of the recording relay BU over a circuit extending from ground over the contacts of relay I324, the inner left front contact of relay I32I to battery through the winding of relay BU. Relay BU upon operating locks over its left contacts under the control of relay I322. With the direct current loop now open at the substation, relay I202 releases followed by the release ofrelay I306 as previously described.

When the off-normal switch assembl 9 again releases to terminate the second frequency impulse, relay I202 again operates thereby causing the reoperation of relay I305 over the circuit previc-u:ly traced. With relay I305 operated and relay I306 unoperated, a circuit is established from ground over the lower front contact of rela I305, the lower back contact of relay I306, the right back contact of relay AD, the No. 2 back contact of relay BD, the No. 2 front contact of relay CD, the No. 2 back contact of relay AU, the No. 3 front contact of relay BU, the No. 4 back contact of relay CU, conductor I334, the No, 4 front contacts of Progress relay I4I1 to battery through the right winding of relay I4I4 of the office code register B. Relay I4I4 upon operating in this circuit looks over its left winding and left contacts to ground on conductor I303 and with the remaining relays of the B register unoperated serves to register the second oflice code letter H.

The operation of relay I305 with relay I306 unoperated also establishes the previously traced circuit for relay I322 which operates after an interval to cause the release of the operated recording relays CD and BU and the release of the transfer relay I32I. When relay I32I releases,

relay I322 also releases.

When the subscriber depresses the key K3 to transmit impulses for the third code digit 3, the off-normal switch assembly 9 is operated momentarily to open the direct current loop at the substation and to connect the generator G to the ubstation line. During the interval that the switch is thus operated the reed R17 is released to transmit an impulse of the frequency b which upon being received in the receiving channel Fb of the sender results in the operation of the channel relay I324 and, with transfer relay I32I not operated, in the operation of recording relay BD over a circuit extending from ground over the contacts of relay I324, the inner left back contact of relay I32I to battery through the winding of relay BD. Relay BD upon operating locks under the control of relay I322 and prepares the circuit of relay I32I as previously described. When the line loop is opened at the substation by the off-normal switch, assembly relay I202 releases and by removing ground from conductor I2I1 permits relay I306 to operate in .the manner previously described, With relays I305 and I306 now both operated and relay I325 operated, a circuit is established from ground over the lower front contact of relay I305, the lower front contact of relay I306, the left contacts of relay I325, conductor I3I2, the right back contact of relay I 406, the right front contact of relay I4I6, to battery through the winding of progress relay I426. Relay I426 operates and locks through its winding and the winding of progress relay I421, over the left contacts of relay I426 and over the back contact of the progress relay (not shown) associated with the thousands digit register and corresponding to progress relay I421 to ground on conductor I303. Progress relay I421 being shunted does not opcrate so long as ground remains connected to conductor I3I2.

At the end of the first impulse for the third code digit with th off-normal switch assembly 5 restored, the transmission of the frequency 1) ceases, channel relay I324 releases and the direct current loop is reestablished at the substation resulting in the reoperation of relay I202 and reconnection of ground to conductor I2I1. As before described, relay I306 is now held operated to this ground and relay I305 is shunted and releases. With relay I305 released and relay I306 operated a circuit for transfer relay I32I, previously prepared through the operation of recording relay ED, is completed and relay I32I operates and looks as previously described under the control of relay I322. Relay I305 upon releasing also removes ground from conductor I3I2 whereupon progress relay I421 operates in th locking circuit of relay I426; connects the windings of the relays of the C code digit register to conductors I33I, I332, I334, I335 and I330'eX- tending to contacts of the recording relays and at its right back contact opens the locking circuit of relays I4I6 and I4I1 which now release since their operating circuit was opened upon the removal of ground from conductor I3 I 2.

Upon the up stroke of the depressed key K3 the ofi-normal switch assembly 9 is again operated momentarily to open the direct current loop at the substation and to connect the generator G to the substation line. During the interval that the switch is thus operated the reed Rb is released to transmit the frequency b which upon being received in the receiving channel PI) of the sender results in the operation of the channel relay I324 and, with transfer relay I32I operated, in the operation of recording relay BU. Relay BU upon operating looks over its left contacts under the control of relay I322.

When the off-normal switch assembly 9 again releases to terminate the second frequency impulse, relay I202 again operates thereby causing the reoperation of relay I305 over the circuit previously traced. With relay I305 operated and relay I306 unoperated, a first circuit is established from ground over the lower front contact of relay I305, the lower back contact of relay I306, the right back contact of relay AD, the No.

l 3 right front contact of relay BD, th No. 3 right back contact of relay CD, the No. 3 right back contact of relay AU, the No. 5 right front contact of relay BU, the No. 6 right back contact of relay CU, conductor I33I, the No. 2 left contacts of progress relay I421 to battery through the right winding of relay I42I of the code digit register C, and a second circuit is established from ground applied over the right back contact of relay AD, the No. 4 right front contact of relay BD, the No. 4 right back contact of relay CD, the No. 4 right back contact of relay AU, the No. 7 right front contact of relay BU, the No. 5 right back contact of relay CU, conductor I332, the No. 3 left contacts of progress relay I421 to of the code digit register C. Relays I42! and aw -see faz z upen operating'lock over. their left ttmamgs and left contacts to ground on conductor 1 366 and 'with the other relays of the-C "code" digit register 'unoper'ated' serve "to register the third oiii'ce code'digit 3. i

The operation of relay"l3il5 with "relay F306 'unoperated alsoestablishes the previouslytraced circuit of relay 13,22 which operates"after animof the thousands numerical digit 1 two impulses of frequency a are sentire'sulting' in theo'peration 1 of recording'relays A'DaridAU. In response to the keying ofthe hundreds digit 'an'impulse of frequency 0 followed" by an impulse of-frequencies a 'andb are sent're'sultingin the "operation of recording relays CD, AU and BU. Inresponse to the keying of the tens digit 6"an'imp'ulse of frequency 0 followed by an impulseof frequency a arefsent r'esuit'ing'in the operation of recording reIa'ys'CD andAU'and in response to the keying of the units digit Tan impulse offrequency b followed by animpnlse of frequency a. are sent resulting in'the o eration of 'recordingrelays BDand AU.

With recording relays AD and All operated to record th receipt of signal impulses for'the thousands digit 1, then w'hen ground is applied to the right armature cf'relay, AD, a 'circuit'is established over the right front-"contact: of relay AD,the No. 1 right back'contact ofrelay B'D, the N011 right'back contact'ofrela'y CD; the'No. 1 right'front' contactof relay AU," the No; '2 right back contact of relay BU," theINo. Frightbaok contact'of relays CU to conductor f 331 and thence over'the No. 2 left contacts of an operated. progress relay, similar'to relay [401 but associated with the thousands 'dig'it' 'r-'e" ','ister, to/battery through the winding or a re1ay of'that register correspon'dingto relay [48! whereby such relay operates and'locks and 'w'ith'the other relays of suchregister unoperated rgisters the thousands digit 1.

With the" recording relays CD, AU. and EU op.- erated to 'rcordthe'receipt of signal impulses for the hundreds digit Othen-whentgroundlishapplied to the right armature of' relay a. circuit is established over thelright back-contact. of relay AD, the No. 2 right back contactmft relay 3D, the No. 2"right front contact ofrelay CD,.the No. 2 right front contact of relay AU,- theNo. 2 right'front contact of 'relayB'U, the No.-3.= right back contact of relayfCU'to conductor [fill-and thence over'the No. '1 left contactsof -an operated progress relay,- similartorelay Hal but associated with the hundreds. digit register, to battery through the winding er. a-relay df that register'corre'sponding torelay I490? whereupon such'relay operates and locks to register the hundreds digit 0.

With recording relays CD and AUoperate'dto record the receipt ofsignalimpulses for the tens digit 6, then when ground i applied to-the right armature of relay AD. afirst circuit-is completed overi the right back contact-of relay An-the No. 2 right back contact of relay BD,the"N0. Z right front contact of relay CD, the-'No. 2 r ight front contact of relay AU,N0.' 2right back contactof relay EU, the No."6 right backponta'ctpf relay CU; conductor l 33+ and thence over the'No. 2 left contacts oian operatecl-progressrelay, similar to relay- I491 but associated with 'thetens "digit 12 register; to 'battery" through unwinding of a relay of-such register corresponding tc-relay l4lll --wnereupon such relay operates an'dqocks. A-second= circuitis also established from ground apfpliedover therfg'ht ba'ck'contact'or relay All-the No. 2 right "back-contact of relay-ED, the No; 6

right front cont-act of-relay-CD, the-No. "6 rlg'ht front contact of relay ltlil, the No. 4 right back "contact or-relay BUgtl-ie No. 1 right back contact "1'0 of: relay 0U; conductor |=335andthence over the No. '5" leftcontactsof ancperated'progress relay, similar-to rclayMU-l but associatedwith the-tens digit register; 'to battery through the-winding of "a relay of -'that register corresponding to relay l4ll5 which 'the'reupon-'operates-and 1 looks; With these two register relays operated and the other relays of 3 the tens digit register unoperated, the tens digit 6 is registere'd.

-With recording relays BD an'd- AU operated fto record' -the receipt of-=signalimpulses for-the unit's dig'it'W; "then when ground is' applied to the 'right'arm'ature'of relay'AD; a first circuit is comthe No: 4*right frozit contact "of relay BD, the No. '4' right back Contact of relay CD, the 'NO. 4r'ight front contact ofrelay -AU, the-'Noafiwi'ght back ofrelay-BD, theNo. itilg'htb a'ewcontact of relay eDjthe N'o; 3Ti'ght frbht COntaCtOf-rla-y AU, the Nox' lf'rig'ht hackccntact "offrelayBU; the? No. 1 righvba'ckcontactof'-"relay CU,'fco1rductor- [-335 and thencepver theiloffi contacts"of relay flfi'l to, battery through the rihtwir'rding ofrelay 1-465 of the,"units"diait register U; Relays-M62 and I865? uponoperating lock over their left windings and 'left*'conta:cts' to ground on "conductor' l3ll3-'anfdtwith' thefotherfrclays 'or-this regi'ster unopera'tedjserve toi're'gi'sterthe'units digit"I.

Allof the digits or the wantedflirrefmrmber keyed by the subscriber. arencw'reg'istered'irr the sender. emf the "sender" may'prceeed" to: control selector. switches" to extend a connection over the" districtselector"-s"and"tover otherselectors, notjs'howrr Irr'accordarrce therewith:after"which the seridteriink'SIrlS released toreleasethei's'ender tomakeit availablefcrother calls;

In"theprecedingdiscussrorrth'keylngtarrdreg istration of letters or? digits' having 7 the "digit values 1-, 2', 3:"4,'f6,f'7. aud o. havebeemdescribed. If'ithedigit'fiiis keyed bythepperationof key K5 then an- .impulseo'f frequency ar'lwoul'dbe sent'followew by'an impulseoffrequency :12 resulting in the" operation orrecording'relays "AD and BU. With i theserelaysioperatedi" then wheng'rc'und is applied to the'rigl1tfarmature of*relay AD,".a cir- 'cuit"is"complete'dtover the rlghtfrontf contactTo'f relay the No'if 1- fightback. contact offrelay BD, the "No'. i 1 rightfbackicontact of relay CD, the N0. lrl-ht back contaotbfrelayAU, theNo. 1 right front contactpf'relay BU, the No.1 fright back contact (if: relay CU Ito conductor 5 I335? to cause the"operatiomofiarelaypf a. register, such asrelay i405 oftliefirst codefdi'gitregisterh.

r If the digit 8 'iskeyed"by'theoperationof key K8? therrani impulsebffrequency a is sent followedby an impulseprfrequencyc resulting. in the operatibn offrecording vrelays and'fCU. 'With. tliese'irelaysjoperatdithen, whenrgroundl is applidto mergers-mature of relay AD, a'first 13 circuit is completed over the right front contact of relay AD, the No. 1 right back contact of relay BD, the No. 5 right back contact of relay CD, the No. 5 right back contact of relay AU, the- No. 8 right back contact of relay BU and the No. 6 right front contact of relay CU to conductor I33I; a second circuit is completed over the right front contact of relay AD, the No. 1 right back I contact of relay BD, the No. 1 right back contact of relay CD, the No. 1 right back contact of relay AU, the No. 1 right back contact of relay BU and the No. 2 right front contact of relay CU to conductor I332 and a third circuit is established over the right back contact of relay AD, the No. 1 right back contact of relay BD, the No. 1 right back contact of relay CD, the No. 1 right back contact of relay AU, the No. 1 right back contact of relay BU and the No. 1 right front contact of relay CU to conductor I335. With ground applied to conductors I33I, I332 and I335 relays of a digit register, such as relay I40I, I402, I495 of the first code digit register A are operated to register the digit 8.

If the digit 9 is keyed by the operation of key K9, then an impulse of frequency 1) is sent followed by an impulse of frequency resulting in the operation of recording relays BD and CU. With these relays operated, then when ground is supplied to the right armature of relay AD, a first circuit is completed over the right back contact of relay AD, the No. 3 right front contact of relay BD, the No. 3 right back contact of relay CD, the No. 3 right back contact of relay AU, the No. 5 right back contact of relay BU and the No. 4 right front contact of relay CU to conductor I334 and a second circuit is established from ground over the right back contact of relay AD, the No. 4 right front contact of relay BD, the No. 4 right back contact of relay CD, the No. 4 right back contact of relay AU, the No, 'iright back contact of relay BU and the No. 7 right front contact of relay CU to conductor I335. With ground applied to conductors I334 and I335, relays of a digit register such as relays I404 and I405 of the first code digit register A are operated to register the digit 9.

What is claimed is:

1. In a telephone system, a central oflice, a line incoming thereto, means for generating current of a plurality of difierent frequencies, means for transmitting over said line two impulses of selected frequencies in accordance with any of a plurality of signal values, means at said central omce responsive respectively to said different frequencies, two groups of relays, each group comprising as many relays as there are frequency responsive means, means for rendering one of said groups of relays responsive to said responsive means to register the first impulse of a transmitted signal, and means controlled over said line for rendering the other of said groups of relays responsive to said responsive means to register the other impulse of the same signal.

2. In a telephone system, a, central office, a line incoming thereto, means for generating current of a plurality of different frequencies, means for transmitting over said line two impulses of selected frequencies in accordance with any of a plurality of signal values, means at said central omce responsive respectively to said different frequencies, two groups of relays, each group comp s as many relays as there are frequency responsive means, means for rendering one of said groups of relays responsive to said responsive means to register the first impulse of a transmitted signal, and a transfer relay operable following the operation of any relay of said first group for rendering the other of said groups of relays: responsive to said responsive means to register the other impulse of the same signal.

3. In a telephone system, a central office, a line incoming thereto, means for generating current of a plurality of different frequencies, means for transmitting over said line two impulses of selected frequencies in accordances with any of a plurality of signal values, means at said central office responsive respectively to said different frequencies, two groups of relays, each group comprising as many relays as there are frequency responsive means, means for rendering one of said groups of relays responsive to said responsive means to register the first impulse of a transmitted signal, a transfer relay for renderingsaid one group of relays unres onsive to said responsive means and for rendering the other of said groups of relays responsive to said responsive means to register theother impulse of the same signal, and relay means operative upon the termination of the transmission of the first impulse of a signal to cause the operation of said transfer relays.

4. In a telephone system, a calling line, a central office, means for extending a connection from said line to said oflice, means at the substation of said calling line for generating current of a plurality of different frequencies, means for transmitting over said line two impulses of selected frequencies in accordance with any of the ten digit values, means at said central oflice responsive respectively to said different frequencies, two groups of relays, each group comprising as many relays as there are frequency responsive means, mean for rendering one of said groups'of relays responsive to said responsive means to register the first impulse of a transmitted digit signal, and means controlled over said calling line for thereafter rendering the other of said groups of relays responsive to said responsive means to register the other impulse of the same digit signal.

5. In a telephone system, a calling line, a central office, means for extending a connection from said line to said office, means at the substation of said calling line for generating current of a plurality of different frequencies, a plurality of digit keys associated'with said generating means, means selectively responsive to the operation of said keys in accordance with the ten digit values to transmit an impulse of selected frequency during the down stroke of the operated key and to transmit a second impulse of one or more of saidfrequencies during the up stroke of the operated key, means at said central oflice responsive respectively to said different frequencies, two groups ofrelays, each group comprising as many relays as there are responsive means, means for rendering one of said groups of relays responsive to said responsive means to register the first impulse of a transmitted digit signal, and means controlled over said calling line for thereafter rendering the other of said groups of relays responsive to said responsive means to register the other impulse of the same digit signal.

6. In a telephone system, a calling line, a central ofiice, means for extending a connection from said line to said ofllce, means at the substation of the calling line for generating current of a plurality of different frequencies, means for trans- 

